Leading-edge vortex dynamics and impulse-based lift force analysis of oscillating airfoils

2019 ◽  
Vol 60 (10) ◽  
Author(s):  
Firas F. Siala ◽  
James A. Liburdy
Keyword(s):  
Vortex Dynamics ◽  
Lift Force ◽  
Leading Edge ◽  
Force Analysis ◽  
Leading Edge Vortex ◽  
Edge Vortex

Leading-edge vortex dynamics on a slender oscillating wing

1988 ◽  
Vol 25 (9) ◽  
pp. 815-819 ◽  
Author(s):  
Young-Whoon Jun ◽  
Robert C. Nelson
Keyword(s):  
Vortex Dynamics ◽  
Leading Edge ◽  
Leading Edge Vortex ◽  
Edge Vortex

Scaling law for the lift force of autorotating falling seeds at terminal velocity

2017 ◽  
Vol 835 ◽  
pp. 406-420 ◽  
Author(s):  
Injae Lee ◽  
Haecheon Choi
Keyword(s):  
Numerical Simulation ◽  
Lift Force ◽  
Lift Coefficient ◽  
Scaling Law ◽  
Leading Edge ◽  
Terminal Velocity ◽  
Leading Edge Vortex ◽  
Actuator Disk ◽  
Vortex Theory ◽  
Edge Vortex

We provide a scaling law for the lift force of autorotating falling seeds at terminal velocity to describe the relation among the lift force, seed geometry and terminal descending and rotating velocities. Two theories, steady wing-vortex theory and actuator-disk theory, are examined to derive the scaling law. In the steady wing-vortex theory, the strength of a leading-edge vortex is scaled with the circulation around a wing and the lift force is modelled by the time derivative of vortical impulse, whereas the conservations of mass, linear and angular momentum, and kinetic energy across the autorotating falling seed are applied in the actuator-disk theory. To examine the validity of the theoretical results, an unsteady three-dimensional numerical simulation is conducted for flow around an autorotating seed (Acer palmatum) during free fall. The sectional lift coefficient predicted from the steady wing-vortex theory reasonably agrees with that from the numerical simulation, whereas the actuator-disk theory fails to provide an estimation of the sectional lift coefficient. The weights of 11 different species of autorotating falling seeds fall on the scaling law derived from the steady wing-vortex theory, suggesting that even a simple theoretical approach can explain how falling seeds support their weights by autorotation once the circulation from a leading-edge vortex is properly included in the theory.

scholarly journals The vortex wake of a ‘hovering’ model hawkmoth

1997 ◽  
Vol 352 (1351) ◽  
pp. 317-328 ◽  
Author(s):  
Coen van den Berg ◽  
Charles P. Ellington
Keyword(s):  
Lift Force ◽  
Three Dimensional ◽  
Axial Flow ◽  
Leading Edge ◽  
The Body ◽  
Tip Vortex ◽  
Vortex Rings ◽  
Leading Edge Vortex ◽  
Edge Vortex ◽  
Visualization Experiments

Visualization experiments with Manduca sexta have revealed the presence of a leading–edge vortex and a highly three–dimensional flow pattern. To further investigate this important discovery, a scaled–up robotic insect was built (the ‘flapper’) which could mimic the complex movements of the wings of a hovering hawkmoth. Smoke released from the leading edge of the flapper wing revealed a small but strong leading–edge vortex on the downstroke. This vortex had a high axial flow velocity and was stable, separating from the wing at approximately 75 % of the wing length. It connected to a large, tangled tip vortex, extending back to a combining stopping and starting vortex from pronation. At the end of the downstroke, the wake could be approximated as one vortex ring per wing. Based on the size and velocity of the vortex rings, the mean lift force during the downstroke was estimated to be about 1.5 times the body weight of a hawkmoth, confirming that the downstroke is the main provider of lift force.

scholarly journals Numerical Analysis of Leading-Edge Vortex Effect on Tidal Current Energy Extraction Performance for Chord-Wise Deformable Oscillating Hydrofoil

2019 ◽  
Vol 7 (11) ◽  
pp. 398
Author(s):  
Xu ◽  
Zhu ◽  
Guan ◽  
Zhan
Keyword(s):  
Surface Pressure ◽  
Pressure Difference ◽  
Lift Force ◽  
Leading Edge ◽  
Energy Extraction ◽  
Tidal Current Energy ◽  
Leading Edge Vortex ◽  
Edge Vortex ◽  
Extraction Performance ◽  
Attached Vortex

To improve the energy extraction performance of the oscillating hydrofoil, the lift force that acts on the oscillating hydrofoil is analyzed. The pressure difference between the oscillating hydrofoil‘s opposing surfaces is dominant to generate the lift force. Forming and shedding of the leading-edge vortex from the hydrofoil surface determines the pressure difference between the opposing surfaces of the oscillating hydrofoil. In this paper, the hydrofoil with different chord flexibility coefficients and maximum offset at the trailing edge are analyzed to obtain the power coefficient, lift coefficient, and moment coefficient of the oscillating hydrofoil. The influence mechanism of chord-wise deformation of the oscillating hydrofoil on the energy extraction performance is explored. According to the Kutta–Joukowsky condition and the Stokes’ theorem, the relationship between the attached vortex on the hydrofoil and the surface pressure of the hydrofoil, the surface pressure difference of the hydrofoil, and the lift force that acts on the hydrofoil are investigated. By quantifying the vortex intensity, the ascending-shedding process of the attached vortex on the hydrofoil is characterized. Finally, the complete influence chain among the chord-wise flexure, the attached vortex on the hydrofoil, and the energy extraction performance of the oscillating hydrofoil is established.

Leading-Edge Vortex Dynamics on Plunging 2D and 3D Wings

2022 ◽  
Author(s):  
Onur Son ◽  
Zhijin Wang ◽  
Ismet Gursul
Keyword(s):  
Vortex Dynamics ◽  
Leading Edge ◽  
Leading Edge Vortex ◽  
Edge Vortex ◽  
2D And 3D

Unsteady force generation and vortex dynamics of pitching and plunging aerofoils

2012 ◽  
Vol 709 ◽  
pp. 37-68 ◽  
Author(s):  
Yeon Sik Baik ◽  
Luis P. Bernal ◽  
Kenneth Granlund ◽  
Michael V. Ol
Keyword(s):  
Strouhal Number ◽  
Vortex Dynamics ◽  
Angle Of Attack ◽  
Leading Edge ◽  
Leading Edge Vortex ◽  
Reduced Frequency ◽  
Unsteady Force ◽  
Edge Vortex ◽  
Effective Angle ◽  
Flow Evolution

AbstractExperimental studies of the flow topology, leading-edge vortex dynamics and unsteady force produced by pitching and plunging flat-plate aerofoils in forward flight at Reynolds numbers in the range 5000–20 000 are described. We consider the effects of varying frequency and plunge amplitude for the same effective angle-of-attack time history. The effective angle-of-attack history is a sinusoidal oscillation in the range $\ensuremath{-} 6$ to $2{2}^{\ensuremath{\circ} } $ with mean of ${8}^{\ensuremath{\circ} } $ and amplitude of $1{4}^{\ensuremath{\circ} } $. The reduced frequency is varied in the range 0.314–1.0 and the Strouhal number range is 0.10–0.48. Results show that for constant effective angle of attack, the flow evolution is independent of Strouhal number, and as the reduced frequency is increased the leading-edge vortex (LEV) separates later in phase during the downstroke. The LEV trajectory, circulation and area are reported. It is shown that the effective angle of attack and reduced frequency determine the flow evolution, and the Strouhal number is the main parameter determining the aerodynamic force acting on the aerofoil. At low Strouhal numbers, the lift coefficient is proportional to the effective angle of attack, indicating the validity of the quasi-steady approximation. Large values of force coefficients (${\ensuremath{\sim} }6$) are measured at high Strouhal number. The measurement results are compared with linear potential flow theory and found to be in reasonable agreement. During the downstroke, when the LEV is present, better agreement is found when the wake effect is ignored for both the lift and drag coefficients.

Flight

2018 ◽  
Author(s):  
Anders Hedenström
Keyword(s):  
Bird Species ◽  
Leading Edge ◽  
Micro Air Vehicles ◽  
Leading Edge Vortex ◽  
Confined Spaces ◽  
Unsteady Aerodynamic ◽  
Maneuvering Flight ◽  
Edge Vortex ◽  
Lifting Surfaces ◽  
Animal Flight

Animal flight represents a great challenge and model for biomimetic design efforts. Powered flight at low speeds requires not only appropriate lifting surfaces (wings) and actuator (engine), but also an advanced sensory control system to allow maneuvering in confined spaces, and take-off and landing. Millions of years of evolutionary tinkering has resulted in modern birds and bats, which are achieve controlled maneuvering flight as well as hovering and cruising flight with trans-continental non-stop migratory flights enduring several days in some bird species. Unsteady aerodynamic mechanisms allows for hovering and slow flight in insects, birds and bats, such as for example the delayed stall with a leading edge vortex used to enhance lift at slows speeds. By studying animal flight with the aim of mimicking key adaptations allowing flight as found in animals, engineers will be able to design micro air vehicles of similar capacities.

Flow criticality governs leading-edge-vortex initiation on finite wings in unsteady flow

2021 ◽  
Vol 910 ◽  
Author(s):  
Yoshikazu Hirato ◽  
Minao Shen ◽  
Ashok Gopalarathnam ◽  
Jack R. Edwards
Keyword(s):  
Unsteady Flow ◽  
Leading Edge ◽  
Leading Edge Vortex ◽  
Edge Vortex

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